Driving electro-optic displays

ABSTRACT

The technology described in this document may be embodied in a method for controlling a display element. The method includes setting a first drive voltage configured to drive a first terminal of the display element such that the first drive voltage is set to a higher value than a second drive voltage configured to drive a second terminal of the display element. The first and second drive voltages can be configured to cause the display element to present a first display state. The method also includes performing adjustments to the first drive voltage and the second drive voltage such that the first drive voltage is less than the second drive voltage. The adjustments are configured in accordance with whether the display element is to present a second display state different from the first display state.

TECHNICAL FIELD

This application is directed to drivers for electro-optic displays.

BACKGROUND

Electro-optic displays such as electrochromic (EC) displays are examplesof displays that have two or more display states (e.g., stable displaystates) differing from one another in at least one optical property. Theoptical property is typically color perceptible to the human eye.Application of electric fields may cause such displays to go from onedisplay state to another. Examples of such display states include avisible or colored state, and a clear state or black state. For example,bistable displays feature two stable display states. Because power isonly consumed when the display state is changed, EC displays lendthemselves well to battery-powered application where conserving energyfrom limited resources is paramount.

SUMMARY

In one aspect, this document features a method of controlling a displayelement. The method includes setting a first drive voltage configured todrive a first terminal of the display element such that the first drivevoltage is set to a higher value than a second drive voltage configuredto drive a second terminal of the display element. The first and seconddrive voltages can be configured to cause the display element to presenta first display state. The method also includes performing adjustmentsto the first drive voltage and the second drive voltage such that thefirst drive voltage is less than the second drive voltage. Theadjustments are configured in accordance with whether the displayelement is to present a second display state different from the firstdisplay state.

In another aspect, this document features a system that includes a firstdriver, a second driver, and a controller. The first driver configuredto drive a first terminal of a display element, and the second driverconfigured to drive a second terminal of the display element. Thecontroller is configured to provide one or more control signals to thefirst and second drivers such that the control signals cause the firstdriver to generate a first drive voltage and cause the second driver togenerate a second drive voltage. The first drive voltage is higher thanthe second drive voltage, and the first and second drive voltages areusable by the display element to present a first display state. Thecontroller is also configured to provide one or more adjustment signalsto the first and second drivers such that the adjustment signals causeadjustments to the first drive voltage and the second drive voltage suchthat the first drive voltage is less than the second drive voltage. Theadjustments are configured in accordance with whether the displayelement is to present a second display state different from the firstdisplay state.

In yet another aspect, this document features one or moremachine-readable storage devices that have encoded thereon computerreadable instructions for causing one or more processors to performvarious operations. The operations include setting a first drive voltageconfigured to drive a first terminal of the display element such thatthe first drive voltage is set to a higher value than a second drivevoltage configured to drive a second terminal of the display element.The first and second drive voltages can be configured to cause thedisplay element to present a first display state. The operations alsoinclude performing adjustments to the first drive voltage and the seconddrive voltage such that the first drive voltage is less than the seconddrive voltage. The adjustments are configured in accordance with whetherthe display element is to present a second display state different fromthe first display state.

Various implementations of the above aspects can include one or more ofthe following features.

The first drive voltage can be set to a higher value than a second drivevoltage during a first time period, and the adjustments can be performedduring a second time period following the first time period. During thefirst time period, a control signal can be provided for operating aswitch that connects the second terminal to a power rail set at thesecond drive voltage. During the second time period, a control signal(also referred to as a connection signal) can be provided for operatinga switch that connects the second terminal to a power rail set at thesecond drive voltage. The control signal can be provided responsive todetermining that the display element is to present the second displaystate. The first drive voltage and the second drive voltage can beadjusted such that the first drive voltage is higher than the seconddrive voltage during a third time period that follows the second timeperiod. During the third time period, a second control signal (orconnection signal) can be provided, wherein the second control signalcauses the switch to disconnect the second terminal from the power railset at the second drive voltage. The second control signal can beprovided responsive to determining that the display element is topresent the second display state. The first terminal can be a commonterminal, and the second terminal can be a pixel terminal of the displayelement. The first display state can represent a clear state of thedisplay element, and the second display state can represent a coloredstate of the display element.

In some implementations, the technology described herein may provide oneor more of the following advantages.

By providing two separately adjustable voltage outputs, the technologydescribed herein may allow for generating various differential voltagesbetween the two outputs. For example, for a display element needing +3Vfor setting and −3V for clearing, the two-output drive system can use a3V power source to generate all the requisite drive voltages. This mayobviate the need for a three-output drive system (which are kept fixedat 6V, 3V, and 0V, respectively), thereby potentially reducing powerconsumption and bulk (e.g., of additional power sources and/or boostcircuitry) of the corresponding device. This may also allow the drivesystem to be controlled by microcontrollers without using additionalpower circuitry, thereby producing advantageous effects in the cost/sizeof the corresponding device.

DESCRIPTION OF DRAWINGS

FIGS. 1A and 1B illustrate examples of a wearable device that can beused for tracking and saving information about time between clinicalinterventions at a medical facility.

FIG. 1C illustrates activation patterns of display elements within adisplay of the wearable device.

FIG. 2A is a schematic illustration of a two-output driving scheme for adisplay element.

FIG. 2B illustrates a timing diagram associated with the driving schemeof FIG. 2A.

FIG. 3 illustrates an example scheme for displaying digits usingmultiple display elements.

FIG. 4 is a schematic diagram representing an example of a circuit usedfor driving multiple display elements.

FIG. 5 is a schematic diagram representing one particular example of acircuit used for driving multiple display elements.

FIG. 6 illustrates a flowchart.

FIG. 7 illustrates an example of a computing device.

DETAILED DESCRIPTION

The advent of wearable technology has produced various types of wearabledevices for a wide range of applications. Some wearable devices, e.g.,electronic wristbands developed for clinical settings, are intended tobe light-weight, low-cost, low-power, and/or potentially disposable.Such wearable devices often have displays that need to be driven usingdrivers that are power-efficient as well as lightweight. Describedherein is a driver system that may be suitable for driving displayelements in power-constrained applications. While the description belowprimarily uses examples of wearable devices and displays used in suchwearable devices, the technology can be used for various otherapplications where multiple drive voltages are needed for drivingelectronic components.

FIGS. 1A and 1B illustrate a wearable device 100 that can be used fortracking and saving information about time between clinicalinterventions at a medical facility. For example, the wearable devicecan be used to keep track of how long a patient has been waiting to seea doctor, receive assistance at a medical facility, etc. In thisexample, the wearable device 100 includes a display 110 to present acounter indicative of a duration of time, and to present information ontime (e.g., number of minutes) between interventions as documentedduring an emergency event. The wearable device 100 also includes a band120 that can wrap around the wrist of the patient, and can be secured tothe wrist using a fastening mechanism such as the button 125 and thehole 127. In some implementations, the button 125 and the hole 127 canprovide additional functionality such as an activation mechanism for thedisplay 110. For example, the button 125 and the hole 127 can includecircuitry such that once the button is pressed onto the hole for longerthan a predetermined duration (e.g., a few seconds), a control signal issent to the display 110 to activate the display. Once the display isturned on, a count can be initiated (for example, with starting digit130) that increments to reflect the passage time.

The examples in this document primary refer to electro-optic displayssuch as electrochromic (EC) displays. EC displays function based on theelectrochromism effect, which is an effect observable in some materials(often referred to as electrochromic materials) that change color, forexample, when a burst of charge causes electrochemical redox reactionsin the materials. While this document primarily uses examples of ECdisplays, the technology described herein may be used for other types ofdisplays, including other types of reflective displays, transflectivedisplays, transmissive displays, and emissive displays. Examples ofdisplay technologies that may use the described technology includeelectroluminescent displays, electrophoretic displays, cholestericdisplays, electrowetting displays, liquid crystal displays (LCDs) (e.g.,twisted nematic LCDs, super-twisted nematic LCDs, ECB LCDs, cholestericLCDs, ferroelectric LCDs, vertically-aligned LCDs, in-plane switchingLCDs), organic light emitting diode displays, plasma displays, or otherdisplays that are driven using two or more drive voltages. The display110 can be configured to present various types of information bycorresponding arrangements of one or more display elements 132. As shownin FIG. 1B, the display 110 includes a plurality of display elements torepresent an integer digit (e.g., seven individual segments, each ofwhich is implemented using a display element 132). Some of the displayelements can be arranged such that various sets of the display elementscan be selectively activated (e.g., set to a colored display state) ordeactivated (e.g., set to a different color display state, a whitedisplay state, a black display state, or a clear display state) todisplay one or more digits. In some implementations (e.g., for ECdisplays), the display state can be stable. In such cases, energy isapplied to effect a change in the display state, but the display elementmaintains a display state even when the source of the energy is removed.This is referred to as the persistence effect.

In the examples of FIGS. 1A and 1B, the display 110 includes displayelements arranged to present three digits, each of which include sevendisplay elements capable of representing the digits “0” to “9”. In someimplementations, one or more display elements can also be used topresent other types of information separate from integer digits. Forexample, the display 110 can include one or more display elements161-164 that represent the number of stored time values. To provide suchfunctionality, the wearable device 100 includes a save button 140 forstoring, at various time points, time values as tracked by the wearabledevice 100. For example, a count presented on the display 110 can bestored by pressing the save button 140 for a predetermined duration oftime (for example, 2 seconds). In some implementations, upon storing avalue (e.g., the last displayed value) the count being presented on thedisplay 110 may reset (e.g., to a zero value). In some implementations,the save operation may store the count without resetting the counter.For other functionality, the wearable device 100 may have a preset time(which may be referred to as an “ideal reset time”) after which thedevice resets. For example, the device 100 can be configured to resetevery 20 minutes. The number of reset points (or time points at whichthe time values are stored) can be visually presented on the display 110using the display elements 161-164. In some implementations, one of thedigits of the display 110 can also be used to present the reset points.

The display elements 161-164 can be used to visually present the numberof reset points (and/or the number of stored time values) in variousways. Example activation patterns (160 a-160 n, 160 in general) for thedisplay elements 161-164 are shown in FIG. 1C. For example, when no timevalues are stored, none of the four display elements 161-164 isactivated. The activation pattern 160 a represents this scenario. Thefirst reset point can be represented using the activation pattern 160 b,and subsequent reset points can be represented using the activationpatterns 160 c-160 n. Other schemes of activating the display elements161-164 are also possible. For example, the display elements can be usedto represent binary digits (e.g., with an activated or colored conditionrepresenting a binary 1, and a clear condition representing a binary 0).

Referring again to FIGS. 1A and 1B, in some implementations the wearabledevice 100 includes a cycle button 150. Activating the cycle button 150(e.g., by pressing and holding the button) can initiate a managementmode of the wearable device 100 in which all the stored reset pointsand/or corresponding time values are displayed sequentially. The cyclebutton 150 can be held at any time after the display 110 has beenactivated to place the device 100 into the management mode. For eachtime value presented on the display 110, the corresponding reset pointcan also be presented using, for example, an associated activationpattern 160 (shown in FIG. 1C). Each stored time value can be displayedfor a predetermined duration (for example, a few seconds) before movingto the next stored time value. After the last stored time value isdisplayed, the display may continue to cycle through the stored timevalues once again starting from the first stored time value. In someimplementations, activating the management mode can cause a suspensionof the time tracking functionality of the device 100. For example, whilein the management mode, the wearable device 100 may not continue to runthe counter, store a new time value, etc. Deactivating the cycle button150 (e.g., by releasing the button) can terminate the management mode.

In some implementations, the display elements 132 can be EC displayelements. EC display elements having low power consumption and goodcontrast may in some cases be advantageous for the wearable device 100.By activating and deactivating various sets of display elements 132,integer digits and other types of information can be presented on thedisplay 110. Each display element 132 can be activated (set to a colorstate) or deactivated (set to a clear state) by applying predeterminedvoltages at two terminals (e.g., electrodes) of the display element 132.These two terminals are often individually referred to as a pixelterminal and a common terminal, respectively. In some cases, the commonterminal is maintained at a reference potential, and +3V or −3V relativeto the reference is applied at the pixel terminal to color or clear,respectively, the display element. This can be done, for example, byconnecting the common electrode or terminal to a voltage line (alsoreferred to herein as a “rail”) maintained at a substantially constantpotential of 3V, and using transistor logic to connect the pixelterminal to either a rail that is maintained at 6V (+3V relative tocommon) to color, or another rail that is maintained at 0V (−3V relativeto common) to clear. However, the batteries, boost circuitry, etc.needed to generate the 6V range, using a three-output drive system maynot always be feasible for portable, lightweight, and low-costelectronics such as that used in the wearable device 100.

The technology described herein provides a two-output drive system inwhich the voltage on each of the two outputs are separately adjustable.Using such a two-output drive system, the voltages on the pixel terminaland the common terminal of a display element 132 can be separatelyadjusted to provide the voltages needed for coloring or clearing thedisplay elements 132. Therefore, rather than using three rails set atfixed voltages, the two-output drive system allows for display elements132 to be set to both colored and clear states using only two adjustablevoltage outputs. For a display element needing +3V for setting and −3Vfor clearing, the two-output drive system can use a 3V power source,thereby reducing power consumption and bulk (e.g., of additional powersources and/or boost circuitry) as compared to a three-output drivesystems requiring a 6V range. This also allows the display elements 132to be controlled by microcontrollers without using additional powercircuitry, which can increase the cost/size of the overall device 100.In addition, the drive system described herein uses the persistenceeffect of EC display elements and avoids consuming power to keep such ECdisplay element colored.

FIG. 2A is a schematic illustration of a two-output driving system 250for driving an individual display element 132 (e.g., one of sevensegments). The drive system 250 includes two drivers 250 a and 250 bthat can independently drive two power rails 210 and 212, respectively.The driver 250 a is configured to set a drive voltage on the power rail210, and the driver 250 b is configured to set a drive voltage on thepower rail 212. The drive voltages on the rails 210 and 212 can beadjusted independently of one another. The display element 132 includesa pixel terminal 211 and a common terminal 213 that can be connected ordisconnected to the rail 210 (also referred to as the pixel rail) andthe rail 212 (also referred to as the common rail), respectively. Theconnection between the pixel terminal 211 and the pixel rail 210 can becontrolled using a switch 214, and the connection between the commonterminal 213 and the common rail 212 can be controlled using a switch215. The switches 214 and 215 can be implemented, for example, usingtransistors that can be switched on and off using control signals from acontroller device such as a microcontroller, microprocessor, digitalsignal processor, etc. When a switch is opened (e.g., turned off), thecorresponding terminal is referred to be in a high impedance state(referred to herein as a high-Z state).

The drive voltages on the pixel rail and the common rail can beindependently adjusted to set the display element 132 in the colored orclear states. For example, to set or color the display element 132 usinga +3V drive voltage, the drive voltage on the common rail 212 is set to0V, and the drive voltage on the pixel rail 210 is set to 3V. Under suchconditions, because the voltage difference between the pixel and commonterminal (V_(PC)) is +3V, the display element 132 is set to coloredstate. To clear or bleach the display element 132 using a −3V signal,the drive voltage on the common rail 212 is set to 3V, and the drivevoltage on the pixel rail 210 is set to 0V. Under this condition, thevoltage difference between the pixel and common terminals (V_(PC)) is−3V, and therefore the display element 132 is set to a clear state. Insome implementations, once the display element 132 is colored orcleared, the pixel terminal and/or the common terminal can beelectrically disconnected from its corresponding rail, for example,using the switches 214 and 215, respectively. Upon being disconnected,the terminal is placed into a high-impedance (high Z) state and thedisplay state of the display element remains substantially unchanged,for example, due to the persistence effect.

FIG. 2B illustrates a timing diagram 255 associated with the drivingsystem of FIG. 2A. The timing diagram 255 shows an example of how adrive voltage 270 on the pixel rail 210 and a drive voltage 275 on thecommon rail 212 are adjusted over time to drive the display element 132to attain different display states. In this example, during the initialtime period 260, both the common terminal 213 and the pixel terminal 213are in the high Z state, and therefore, the display element 132 is inthe persistence state. At time t1, the drive voltage 270 and the drivevoltage 275 are set to 0V and 3V, respectively, and these voltages aremaintained during the time period 262. During the time duration 262,once the drive voltages ramp up/down to the set values, the voltagedifference between the pixel and common rails is V_(PC)=−3V.Accordingly, as soon as the pixel terminal 211 and common terminal 213are connected to the corresponding rails, the display element 132 istaken out of the high-Z state and set to the cleared display state. Thecombination of drive voltages on the pixel rail 210 and the common rail212 during the time period 262 can be considered as a clear pulse of thedriving system 250.

At time t2, the drive voltage 270 and the drive voltage 275 are beingdriven to 3V and 0V, respectively, and these voltages are maintainedduring the time period 264. During the time duration 264, once the drivevoltages ramp up/down to the set values, the differential voltagebetween the pixel and common rails is V_(PC)=3V. Accordingly, thedisplay element 132 is set to the colored display state. The combinationof drive voltages on the pixel rail 210 and the common rail 212 duringthe time period 264 can be considered as a color pulse of the drivingsystem 250.

At time t3, both the pixel terminal and the common terminal areelectrically disconnected from the pixel rail and the common rail,respectively, to set the terminals in a high-Z state. Under thissituation, the display element maintains the color state due to thepersistence effect even if both drive voltages are set to 0V. By nothaving to provide a drive voltage on either rail until a change of stateis required, the two-output drive system can provide significant powerefficiency for wearable devices such as the device 100.

FIG. 3 illustrates an example of displaying digits using multipledisplay elements. In particular, FIG. 3 shows a timing diagramassociated with multiple display elements (i.e., seven elements) tochange a displayed digit from “0” to “1”. During time period 360,display elements 311-316 are in a colored display state, and the displayelement 317 is in a clear display state, and thus the combination of thedisplay elements 311-317 displays the digit “0”. Each of the displayelements 311-317 can be substantially same as the display element 132described above with reference to FIG. 2A. The common terminal of eachof the display elements 311-317 is connected (via a correspondingswitch) to the common drive rail. The trace 320 represents the drivevoltage at the common terminal of each of the display elements 311-317.The pixel terminal of each of the display elements 311-317 is connected(via a corresponding switch) to the pixel drive rail. The traces 321-327represent the drive voltage at the pixel terminals of the displayelements 311-317, respectively. The drive voltages can be generated by atwo-output drive system substantially similar to the drive system 250described with reference to FIG. 2A.

During the time period 360, digit “0” is displayed and the pixel and thecommon terminals of all the display elements 311-317 are disconnectedfrom the corresponding rails, and therefore are in the high Z state. Tochange the change the displayed digit (in this example, from “0” to“1”), the display driver generates a clear pulse to clear each of thedisplay elements 311-316 that was in a colored state during the timeperiod 360. This can include setting the drive voltage in the commonrail to +3V, setting the drive voltage in the pixel rail to 0V, andconnecting each of the display elements 311-316 to the pixel and commonrails via the corresponding switches. This results in a differentialvoltage V_(PC)=−3V for the display elements connected to the rails, andthose elements are therefore set to a clear display state. This isillustrated by the states of the display elements during the time period362. Because the display element 317 was in the clear state during thetime period 362, the pixel terminal of the display element 317 can bemaintained in the high Z state (as indicated by the trace 327).

In order to display the digit “1”, the display elements 313 and 314 eachneeds to be set to a colored display state. This can be initiated attime t5 by setting the drive voltage in the common rail to 0V, settingthe drive voltage in the pixel rail to 3V, and connecting each of thedisplay elements 313 and 314 to the pixel and common rails via thecorresponding switches. This results in a differential voltageV_(PC)=+3V for the display elements connected to the pixel rails, andthose elements are therefore set to a colored display state. The drivevoltages on the pixel terminals of the display elements 313 and 314during the time period 364 are illustrated by the traces 323 and 324,respectively. Because the other display elements (i.e., the displayelements 331, 312, and 315-317 are not set to a colored display state,the switches that connect the corresponding pixel terminals to the pixelrail are changed to (or maintained in) an OFF configuration therebydisconnecting the corresponding pixel terminals from the pixel rail.This is illustrated using the high-Z status of the corresponding traces321, 322, and 325-327, respectively.

In some implementations, even when the switch corresponding to aparticular display element is in an OFF state, a leakage current maystill flow through the display element. Therefore, if there is aresidual charge on the display element, the display element may stillshow some coloration. In the example of FIG. 3, the display elements311, 312, 315 and 316, which were in a colored state during the timeperiod 360, may exhibit a partially colored interim display state duringthe time period 364 even when the display element terminals are in ahigh-Z state. On the other hand, because the display element 317 was ina clear state during time period 360, the amount of residual charge inthe display element may be negligible, and therefore the display element317 may not exhibit the interim display state.

In some implementations, where one or more of the display elementsexhibit the interim display state, a clear pulse may be selectivelyprovided to those particular display elements to forcibly drive theparticular display elements to a clear display state. This can also bedone by selectively providing the clear pulse to all the displayelements that are not intended to be in a colored state (e.g., alldisplay elements that either exhibit the interim state or are in a clearstate already). In the example of FIG. 3, during the time period 364,the display elements 311, 312, 315, and 316 exhibit the interim displaystate, and the display element 317 is in a clear state. A clear pulsecan therefore be sent to the display elements 311, 312, and 315-317 toforcibly clear all display elements but the ones (display elements 313and 314, in this example) that are intended to be in the colored state.This can be initiated at time t6 by setting the drive voltage in thecommon rail to +3V, setting the drive voltage in the pixel rail to 0V,and connecting each of the display elements 311, 312, and 315-317 to thepixel and common rails via the corresponding switches. This results in adifferential voltage V_(PC)=−3V for the display elements connected tothe rails, and those elements are therefore set to a clear displaystate. As illustrated by the portions of the traces 323 and 324 in thetime period 366, the display elements 313 and 314 are disconnected fromthe drive voltage rails such that those display elements are unaffectedby the clear pulse, and continue to display the colored display state.

In some implementations, the time periods 360, 362, 364, and 366 mayhave different time durations. For example, the duration of primaryclear pulse (i.e., the pulse in the time period 362) and the primarycolor pulse (i.e., the pulse in the time period 364) can be about 500ms. The time duration of the secondary clear pulse (i.e., the pulse inthe time period 366) can be about 200 ms. The duration of the timeperiods can depend on various factors, including, for example,environmental humidity, display degradation, display architecture, poweroutput of the logic and battery voltage degradation. In someimplementations, as the performance of the power supply to the drivesystem degrades (for example, by providing lower power outputs), thedisplay elements may require more clearing time. As a result, the timeperiod 362 corresponding to the clearing pulse and the time period 364corresponding to the secondary pulse can increase over time. Forexample, for a degraded power supply, the above time periods canincrease in duration by 1 ms for every 5 minutes the device runs on thedegraded power supply.

FIG. 4 is a schematic diagram representing an example of a circuit 400used for driving multiple display elements (e.g., a set of seven displayelements that can together display different digits). The circuit 400includes a first driver 402 that can be used to set and adjust a drivevoltage on a pixel rail 412. The circuit also includes a second driver404 that that can be used to set and adjust a drive voltage on a commonrail 414. In this example, the drivers 402 and 404 can be individuallycontrolled to set either a 3V or a 0V potential on the pixel rail 412and the common rail 414, respectively. A first control signal isprovided the driver 402 via the control line 442, and a second controlsignal is provided to the driver 404 via the control line 444. The firstand second control signals can be provided, for example, by logiccircuitry or a microcontroller and cause the respective drivers to seteither a 0V or a 3V on the corresponding rails. The drivers 402 and 404can include circuitry (e.g., switches such as transistors) for selectingbetween a 0V and 3V supply.

The circuit 400 also includes switches 451-457 arranged to connect ordisconnect the pixel rail 412 from the corresponding pixel terminals ofthe different display elements via the switch terminals 421-427,respectively. In the example shown in FIG. 4, the switches 451-457include transistors that can be controlled by providing control signalsover the control lines 431-437, respectively, to turn the switches on oroff. In some implementations, the control signals can be provided from acontroller (e.g., a microcontroller, microprocessor, or DSP) to placethe corresponding terminal in or out of a high-Z state. If a particularswitch is turned on by a control signal, the corresponding terminal isconnected to the pixel rail 412. On the other hand, if a particularswitch is turned off by a control signal, the corresponding terminal isdisconnected from the pixel rail, and therefore placed in a high-Zstate.

The circuit 400 also includes a switch 450 arranged to connect ordisconnect the common rail 414 from the common terminals of the variousdisplay elements. In some implementations, the common terminals of thedisplay elements may be electrically connected and coupled to the switchterminal 420, such that all the common terminals of all the displayelements can be taken in and out of a high-Z state simultaneously. Theswitch 450 can include a transistor that can be controlled by providingcontrol signals over the control line 430, to turn the switch on or off.The control signals can be provided from the controller providing thecontrol signals for the pixel terminals. If the switch 450 is turned onby a control signal, the common terminals of all the display elementsare connected to the common rail 414. If the switch 450 is turned off bya control signal, the common terminals of all the display elements aredisconnected from the common rail, and therefore placed in a high-Zstate.

FIG. 5 is a schematic diagram representing one particular example of acircuit used for driving multiple display elements. In this figure, theintegrated circuit 500 is a microcontroller capable of outputting twodrive voltages (0V and 3V) as well as a high-impedance state for threeseparate display elements. Unlike the circuit 400 of FIG. 4, where thecontrol lines 431-437 are connected to switches such as controltransistors that connect power rails to the display, the circuit 500includes control lines 502 that are directly connected to the display toprovide the 0V/3V/high-impedance needed to change or maintain a displaystate. For example, to set a colored display state, the microcontrollercan be programmed to provide 0V on the COMMON pin 503 and 3V on thepin(s) connected to the pixel(s) or display element(s) desired to becolored. Once the colored display state is set, the pixel and COMMONpins may be set to high-impedance states to maintain the color using thepersistence feature of the display element. To clear a display state,the microcontroller can be programmed to provide 3V on the COMMON pin503 and 0V on the pin(s) connected to the pixel(s) desired to becleared. Once cleared, the pixel and COMMON pins may be set tohigh-impedance states. As shown in FIG. 5, the integrated circuit 500may be connected to additional external circuitry used for programmingthe microcontroller and maintaining an accurate time for use in thedevice shown in FIGS. 1A and 1B.

FIG. 6 shows a flowchart depicting an example of a process 600 fordriving a two-output drive system. In some implementations, the process600 can be implemented, at least in part, using a drive system 250described above with reference to FIG. 2A, or using a drive systemincluding the drivers 402 and 404 described with reference to FIG. 4.Implementation of the process 600 can also include use of one or moreprocessing devices such as microcontrollers, microprocessors or DSPs.Operations of the process 600 can include setting a first drive voltageconfigured to drive a first terminal of the display element (610). Thefirst drive voltage can be set to a higher value than a second drivevoltage, wherein the second drive voltage is configured to drive asecond terminal of the display element. In some implementations, thefirst and second drive voltages are configured such that the two drivevoltages in combination cause the display element to present a firstdisplay state. For example, the two drive voltages can be used inconjunction to produce the differential voltage V_(PC) that causescoloring and clearing of display elements 132 described with referenceto FIG. 2A. For example, for an EC display element, the first drivevoltage can be set to +3V and the second drive voltage can be set to 0Vto provide a differential voltage of V_(PC)=−3V. The first and secondterminals can be the common and pixel terminals, respectively of adisplay element.

In some implementations, the first drive voltage is set to a highervalue than a second drive voltage during a first time period to clearthe display element. This can include providing, during the first timeperiod, a control signal for operating a switch that connects the secondterminal to a power rail set at the second drive voltage. The power railcan be substantially similar to the pixel rail 210 described withreference to FIG. 2A, or the pixel rail 412 described with reference toFIG. 4. This can also include providing, during the first time period, acontrol signal for operating another switch that connects the firstterminal to another power rail set at the first drive voltage. The powerrail set at the first drive voltage can be substantially similar to thecommon rail 212 described with reference to FIG. 2A, or the common rail414 described with reference to FIG. 4.

Operations of the process 600 also includes performing adjustments tothe first drive voltage and the second drive voltage such that the firstdrive voltage is less than the second drive voltage (620). Theadjustments are configured in accordance with whether the displayelement is to present a second display state different from the firstdisplay state. For example, if the display element is an EC displayelement that is to be set to a colored state, the first drive voltage(which may be provided on a common rail) can be set to 0V and the seconddrive voltage (which may be provided on a pixel rail) can be set to 3Vto provide a differential voltage of V_(PC)=3V.

Setting the display element to a colored state can also includeproviding a control signal for operating a switch that connects thesecond terminal to a power rail set at the second drive voltage. Forexample, if a particular display element is to be set to a coloredstate, a control signal can be provided to close the switch such thatthe second terminal (e.g., the pixel terminal) of the display element isconnected to the power rail (e.g., the pixel rail) carrying the seconddrive voltage. On the other hand, if the display element is not to beset to a colored state, the switch is kept open, or opened using acontrol signal, such that the second terminal of the display element isdisconnected from the power rail carrying the second drive voltage.

In some implementations, even when the second terminal of the displayelement is disconnected from the power rail carrying the second drivevoltage, the display element may exhibit the interim display state(described above with reference to FIG. 3) due to residual charges onthe element. In such cases, the first drive voltage and the second drivevoltage can be adjusted again such that the first drive voltage ishigher than the second drive voltage. The first and second drivevoltages are adjusted to provide another clearing pulse to the displayelement. This can include connecting the display element to the powerrails via the appropriate switches such that the display element isdriven from the interim state to the clear state. On the other hand, ifthe display element is intended to be maintained in a colored state, thedisplay element is disconnected from the pixel rail such that thedisplay element is unaffected by any clear pulse provided using thepixel rail, and continues to be in the colored state, for example, dueto persistence effect.

FIG. 7 is a schematic diagram of a generic computer system 700. Thesystem 700 can be used for the operations described in association withany of the computer-implemented methods described previously, accordingto one implementation. The system 700 includes a processor 710, a memory720, a storage device 730, and an input/output device 740. Each of thecomponents 710, 720, 730, and 740 are interconnected using a system bus750. The processor 710 is capable of processing instructions forexecution within the system 700. In one implementation, the processor710 is a single-threaded processor. In another implementation, theprocessor 710 is a multi-threaded processor. The processor 710 iscapable of processing instructions stored in the memory 720 or on thestorage device 730 to display graphical information for a user interfaceon the input/output device 740.

The memory 720 stores information within the system 700. In someimplementations, the memory 720 is a computer-readable medium. Thememory 720 is a volatile memory unit in some implementations and is anon-volatile memory unit in other implementations.

The storage device 730 is capable of providing mass storage for thesystem 700. In one implementation, the storage device 730 is acomputer-readable medium. In various different implementations, thestorage device 730 may be a floppy disk device, a hard disk device, anoptical disk device, or a tape device.

The input/output device 740 provides input/output operations for thesystem 700. In one implementation, the input/output device 740 includesa keyboard and/or pointing device. In another implementation, theinput/output device 740 includes a display unit for displaying graphicaluser interfaces.

The features described can be implemented in digital electroniccircuitry, or in computer hardware, firmware, software, or incombinations of them. The apparatus can be implemented in a computerprogram product tangibly embodied in an information carrier, e.g., in amachine-readable storage device, for execution by a programmableprocessor; and method steps can be performed by a programmable processorexecuting a program of instructions to perform functions of thedescribed implementations by operating on input data and generatingoutput. The described features can be implemented advantageously in oneor more computer programs that are executable on a programmable systemincluding at least one programmable processor coupled to receive dataand instructions from, and to transmit data and instructions to, a datastorage system, at least one input device, and at least one outputdevice. A computer program is a set of instructions that can be used,directly or indirectly, in a computer to perform a certain activity orbring about a certain result. A computer program can be written in anyform of programming language, including compiled or interpretedlanguages, and it can be deployed in any form, including as astand-alone program or as a module, component, subroutine, or other unitsuitable for use in a computing environment.

Suitable processors for the execution of a program of instructionsinclude, by way of example, both general and special purposemicroprocessors, and the sole processor or one of multiple processors ofany kind of computer. Generally, a processor will receive instructionsand data from a read-only memory or a random access memory or both. Theessential elements of a computer are a processor for executinginstructions and one or more memories for storing instructions and data.Generally, a computer will also include, or be operatively coupled tocommunicate with, one or more mass storage devices for storing datafiles; such devices include magnetic disks, such as internal hard disksand removable disks; magneto-optical disks; and optical disks. Storagedevices suitable for tangibly embodying computer program instructionsand data include all forms of non-volatile memory, including by way ofexample semiconductor memory devices, such as EPROM, EEPROM, and flashmemory devices; magnetic disks such as internal hard disks and removabledisks; magneto-optical disks; and CD-ROM and DVD-ROM disks. Theprocessor and the memory can be supplemented by, or incorporated in,ASICs (application-specific integrated circuits).

To provide for interaction with a user, the features can be implementedon a computer having a display device such as a touch panel, a CRT(cathode ray tube), or LCD (liquid crystal display) monitor fordisplaying information to the user and a keyboard and a pointing devicesuch as a mouse or a trackball by which the user can provide input tothe computer.

The features can be implemented in a computer system that includes aback-end component, such as a data server, or that includes a middlewarecomponent, such as an application server or an Internet server, or thatincludes a front-end component, such as a client computer having agraphical user interface or an Internet browser, or any combination ofthem. The components of the system can be connected by any form ormedium of digital data communication such as a communication network.Examples of communication networks include, e.g., a LAN, a WAN, and thecomputers and networks forming the Internet.

The computer system can include clients and servers. A client and serverare generally remote from each other and typically interact through anetwork, such as the described one. The relationship of client andserver arises by virtue of computer programs running on the respectivecomputers and having a client-server relationship to each other.

A number of embodiments have been described. Nevertheless, it will beunderstood that various modifications can be made without departing fromthe spirit and scope of the processes and techniques described herein.In addition, the logic flows depicted in the figures do not require theparticular order shown, or sequential order, to achieve desirableresults. In addition, other steps can be provided, or steps can beeliminated, from the described flows, and other components can be addedto, or removed from, the described systems. Accordingly, otherembodiments are within the scope of the following claims.

What is claimed is:
 1. A method of controlling multiple displayelements, the method comprising: setting a first drive voltage on afirst voltage rail configured to drive a first terminal of each of themultiple display elements; setting a second drive voltage, less than thefirst drive voltage, on a second voltage rail configured to drive asecond terminal of each of the multiple display elements, wherein thesecond terminal of each of the multiple display elements is connected tothe second voltage rail via a corresponding switch; providing a firstcontrol signal configured to activate each of a first set of one or moreof the switches to connect corresponding display elements to the secondvoltage rail, such that the voltages on the first and second voltagerails cause the corresponding display elements to present a firstdisplay state; performing adjustments to the first drive voltage and thesecond drive voltage such that the first drive voltage is less than thesecond drive voltage; and providing a second control signal configuredto activate each of a second set of one or more of the switches toconnect corresponding display elements to the second voltage rail,wherein the second set of switches is selected in accordance withwhether the corresponding display elements are to present a seconddisplay state different from the first display state.
 2. The method ofclaim 1, wherein the second drive voltage is less than the first drivevoltage during a first time period, and the adjustments are performedduring a second time period following the first time period.
 3. Themethod of claim 2, wherein the first control signal to each of the firstset of one or more of the switches is provided during the first timeperiod.
 4. The method of claim 2, wherein the second control signal toeach of the second set of one or more of the switches is provided duringthe second time period.
 5. The method of claim 4, further comprisingadjusting the first drive voltage and the second drive voltage such thatthe first drive voltage is higher than the second drive voltage during athird time period that follows the second time period.
 6. The method ofclaim 5, further comprising providing, during the third time period, athird control signal to each of one or more of the switches, the thirdcontrol signal configured to cause the one or more switches todisconnect the corresponding second terminals from the second voltagerail, wherein the third control signal is provided to each of the one ormore switches responsive to determining that the corresponding displayelements are to present the second display state.
 7. The method of claim1, wherein the first terminal is a common terminal, and the secondterminal is a pixel terminal.
 8. The method of claim 1, wherein thefirst display state represents a clear state.
 9. The method of claim 1,wherein the second display state represents a colored state.
 10. Themethod of claim 1, wherein the first terminal of each of the multipledisplay elements is connected to each other, and connected to the firstvoltage rail via a corresponding switch.
 11. A system comprising: afirst driver configured to set a voltage on a first voltage railconnected to a first terminal of each of multiple display elements; asecond driver configured to set a voltage on a second voltage railconnected to a second terminal of each of the multiple display elements,wherein the second terminal of each of the multiple display elements isconnected to the second voltage rail via a corresponding switch; and acontroller configured to: cause the first driver to generate a firstdrive voltage and cause the second driver to generate a second drivevoltage, wherein the first drive voltage is higher than the second drivevoltage, and the first and second drive voltages are usable by thedisplay element to present a first display state, provide a firstcontrol signal configured to activate each of a first set of one or moreof the switches to connect corresponding display elements to the secondvoltage rail, cause adjustments to the first drive voltage and thesecond drive voltage such that the first drive voltage is less than thesecond drive voltage, provide a second control signal configured toactivate each of a second set of one or more of the switches to connectcorresponding display elements to the second voltage rail, wherein thesecond set of switches is selected in accordance with whether thecorresponding display elements are to present a second display statedifferent from the first display state.
 12. The system of claim 11,wherein the second drive voltage is less than the first drive voltageduring a first time period, and the adjustments are performed during asecond time period following the first time period.
 13. The system ofclaim 12, wherein the first control signal to each of the first set ofone or more of the switches is provided during the first time period.14. The system of claim 12, wherein the second control signal to each ofthe second set of one or more of the switches is provided during thesecond time period.
 15. The system of claim 14, wherein the controlleris configured to adjust the first drive voltage and the second drivevoltage such that the first drive voltage is higher than the seconddrive voltage during a third time period that follows the second timeperiod.
 16. The system of claim 15, wherein the controller is configuredto provide, during the third time period, a third control signal to eachof one or more of the switches, the third control signal configured tocause the one or more switches to disconnect the corresponding secondterminals from the second voltage rail, wherein the third control signalis provided to each of the one or more switches responsive todetermining that the corresponding display elements are to present thesecond display state.
 17. The system of claim 11, wherein the firstterminal is a common terminal, and the second terminal is a pixelterminal.
 18. The system of claim 11, wherein the first display staterepresents a clear state.
 19. The system of claim 11, wherein the seconddisplay state represents a colored state.
 20. The system of claim 11,wherein the first terminal of each of the multiple display elements isconnected to each other, and connected to the first voltage rail via acorresponding switch.
 21. One or more non-transitory machine-readablestorage devices having encoded thereon computer readable instructionsfor causing one or more processors to perform operations comprising:setting a first drive voltage on a first voltage rail configured todrive a first terminal of each of multiple display elements; setting asecond drive voltage, less than the first drive voltage, on a secondvoltage rail configured to drive a second terminal of each of themultiple display elements, wherein the second terminal of each of themultiple display elements is connected to the second voltage rail via acorresponding switch; providing a first control signal configured toactivate each of a first set of one or more of the switches to connectcorresponding display elements to the second voltage rail, such that thevoltages on the first and second voltage rails cause the correspondingdisplay elements to present a first display state; performingadjustments to the first drive voltage and the second drive voltage suchthat the first drive voltage is less than the second drive voltage; andproviding a second control signal configured to activate each of asecond set of one or more of the switches to connect correspondingdisplay elements to the second voltage rail, wherein the second set ofswitches is selected in accordance with whether the correspondingdisplay elements are to present a second display state different fromthe first display state.
 22. The one or more machine-readable storagedevices of claim 21, wherein the second drive voltage is less than thefirst drive voltage during a first time period, and the adjustments areperformed during a second time period following the first time period.23. The one or more machine-readable storage devices of claim 22,wherein the first control signal to each of the first set of one or moreof the switches is provided during the first time period.
 24. The one ormore machine-readable storage devices of claim 22, wherein the secondcontrol signal to each of the second set of one or more of the switchesis provided during the second time period.
 25. The one or moremachine-readable storage devices of claim 24, further comprisinginstructions for adjusting the first drive voltage and the second drivevoltage such that the first drive voltage is higher than the seconddrive voltage during a third time period that follows the second timeperiod.
 26. The one or more machine-readable storage devices of claim25, further comprising instructions for providing, during the third timeperiod, a third control signal to each of one or more of the switches,the third control signal configured to cause the one or more switches todisconnect the corresponding second terminals from the second voltagerail, wherein the third control signal is provided to each of the one ormore switches responsive to determining that the corresponding displayelements are to present the second display state.
 27. The one or moremachine-readable storage devices of claim 21, wherein the first terminalis a common terminal, and the second terminal is a pixel terminal. 28.The one or more machine-readable storage devices of claim 21, whereinthe first display state represents a clear state.
 29. The one or moremachine-readable storage devices of claim 21, wherein the second displaystate represents a colored state.
 30. The one or more machine-readablestorage devices of claim 21, wherein the first terminal of each of themultiple display elements is connected to each other, and connected tothe first voltage rail via a corresponding switch.